Improve test infrastructure #5

Currently our cmake project has no tests (in the way cmake understands them). It does however have a tests target that can be executed from the IDE to run sketchup and load them. You currently must have testup installed in sketchup to run them.

Suggested improvements:

• Add testup-2 as a submodule
• modify the tests target
  • rename to avoid confusion with cmake tests predefined target
• add cmake test to project via add_test
  • Add commands to the test that
    • Launch SketchUp
    • require testup (headless with no gui, since this would have to be built)
    • require our test files
    • run testup tests (generating a json file of some sort)
    • close sketchup
    • check the json and exit non zero if not all ok

In an ideal world we could actually run these tests with github actions, but I don't believe it is worth the dev effort at this stage